Process of preparing nitro azo compounds



Patented May 18 1948 MroUnns Edward Franklin Degering, La Fayette, Ind., and

Charles F. Feasley, Thorofare, N. J., assignor's' to Purdue Research Foundation, La Fayette,

Ind., a corporation of Indiana No Drawing. Application October 2, 1942,. I

The present invention relates to certain crystalline nitro azo compounds and to a process of producing nitro azo compounds. More particu- 1a rly it is concerned with a process of preparing nitro azo compounds wherein a ring-substituted.

primary aromatic amine, which forms a diazo compound stable towards the alkaline aqueous medium employed in the subsequent coupling reaction, is first diazotized in an -"acid medium, the resulting diazonium salt solution is then mixedwith a low-molecular weight secondary nitroalkane in a cooled aqueous medium of alkaline reaction containing sufficient caustic alkali to neutralize said diazonium .salt solution and to produce a pH at least as high as that of an aqueous solution of an alkali metal salt of said nitroalkane in order to ensure maintenance of the nitroalkane in the form of its alkali metal salt during the resultingcoupling reaction, followed, by recovery of the nitro azo compound thusformed. 1 I

By the expression ring-substituted primary aromatic amine as used above we-mean amines having the general formula Ar -Nl lz, wherein Ar may represent a heteroaryl radical, such'as 7 the pyridine or thiazoleradicals, or one of the following radicals: I

'SOaM j i cy f o wherein X representseither alkyl, alkoxy, -halo gen, --COO M,-NO-z, SO3M, or NHCCH3; Y may be alkyl, halogen, NO2, SO3M, or hydrogen; andZ may represent halogen or hydrogen, and M is either hydrogen or analkali metal.

As examples of the nitro azc compounds which may be prepared bythe processdefined above then may be mentioned the -acetoaminoben- Serial n 460,550 4 Claims. ,{(Cl. 260-174) azo-nitroalkanes which have the following structural formulas respectively:

alkyl p ulkyl In accordance with the present invention,

compounds of the type represented by the original generic formula are prepared by diazotizing thedesired aromatic monoor diamine in an acid medium and, thereafter, coupling the diazotized amine with the salt of a secondary nitroparaflin. Specifically, the aromatic monoordiamine is firstdiazotized in an acid medium. after which the concentration of base therein ismade equal to or slightly greater than that of the alkaline aqueous secondary nitroparaffin solution by adding the said diazotized solution to a relatively strong solution of a suitable base, such as sodium or potassiumhydroxldes. This quantity produces a total quantity of base in the reaction medium 'of 'double'the equivalent of the nitroparafiin used, that is, atleast 100% excess'of base. Immediately after this step, an aqueous solution of .an alkali or alkaline earthmetal salt of a secondary nitro-parafiin is added to the diazotized amine solution, said nitroparaffin salt 7 being "preferably" added theretoina ratio of one mole of-the salt per amine group'present in the original aromatic amine.

this connection we have found that the coupling of the secondary nltroparaffin salt with the dia z otized aromatic amine must be efiectedpin a mediumliaving a pH equal to or slightlyrgreat'er 6 v thanthe pH oftheconcentrated secondary nitroa'raffiri salt solution used. j Expressed in another mannenit may be saidv thatthe reaction should be, carriedfoutunder conditions where the equizeneazonitroalkanes, and the "4,4 biphenyl-bisg5 librium, represented bythe equation is displaced toward the right, i. e., under conditions favoring salt formation, that is the alkali content or pH of the coupling medium must be sufiiciently high to maintain the nitroparafiin in salt form during the coupling reaction. It was previously known to us that the pH of the meby maintaining the pH of the" reaction medium".

within the above-specified'range,nitro azoxc'ompounds of the aforesaid ty-pemay be produced and are solids atordinary temperatures, may be filtered from a cold isolated in a form sufiic-iently jority of technical uses. 7

The resulting products, which pure for. the masolution and recrystallized from a suitable solvent such as ethyl alcohol. The normally liquid products may, in general, be purified by distillation under vacuum. However, certain of these such as, for example, hydrochloric, nitric, phosphoric, sulfuric, acetic, and the like. The temperature at which diazotization may be efiected can vary from between about 5C. to not in substantial excess of.30 (1., depending upon the particular amine being diazotized; while the solvent employed may be any of several liquids or mixtures thereof in which the final product is substantially insoluble. However, in the majority .of instances We prefer to use water.

The examples which follow are illustrative of the scope of our invention. However, it is to be 7 understood that such examples are not to be conrespect.

sidered as limiting the present invention in any EXAMPLE I A solution of 17.2 parts of p-bromoaniline in 35.7 parts of 38 per cent hydrochloric acid and 62.5 parts of water was diazotized at 0 C. by the dropwise addition .of an aqueous solution containing 7; parts of. sodium nitrite. The diazomaterials decompose rather rapidly under such It is tobe noted that any compound containing morethan one secondary nitro group, with one hydrogen atom on each carbon atom holding a nitro group, will couple with one equivalent of diazonium salt) and/or hydroxide per secondary .nitro group in the compound, and it is'tobe further understood that the term secondary nitroparafrln includes such compounds. 7

The aromatic amines which'may be employed in our process constitute a wide variety. of substituted and unsubstituted aromaticmonoamines and aromatic diaminesand as examples of such compounds there fmay be mentioned sulfanilic acid, l aminobenzene Byl-disulfonic acid, p-nitroaniline, p-aminobenzoic .acid, Z-naphthyl- By secondary nitro- 1 amine-fi-sulfonic acid, i-aminoe3 nitrobenzenesulfonic acid, '4-aminoazobenzene-4-si1lfonic acid, 'o-nitroaniline, m-nitroaniline, 4-nitro 2-' 1 aminotoluene, peaminoacetanilide, o-chloroaniline, o-bromoaniline, 2,5-dichloroaniline, 2,4,6- tribrom'oaniline, p-toluid-ine, O-afil'i'lillObEIlZOlC acid, p-aminoazobenzoic acid, beta-naphthylamine,

2,4-diaminotol1iene, 2,4-dinitroaniline, 'l-phenyl 1 2,3-dimethyl-4-aminoe5-pyrazolone, S-aminoin 'dazole, 2-amino-4-methy1thiazole, 2-aminopyridine, 3-aminopyridine, .o-anisidine, m -anisidine,

p-anisidine, and the like.

In general, it may be said that any aromatic amino compound capable of being diazotized may be employed in our process for the preparation of the novel nitro azo compounds of the present invention, providing, of course, thatnoappre-f ciable' reaction occurs between-one or more molecules ofthe diazotized amine during the process,

that is, the diazotiz'ed amine must belstable in tized solution was poured into a solution con- 'sisting of 20.7 parts of sodium hydroxide, 250

parts of water, and 200 parts of cracked ice. A solution of 8.9 parts of Z-nitropropane in 4 parts of sodium hydroxide and 125 parts of water was immediately added to the slightly alkaline ,diazotizedsolution with thorough agitation. The resulting solution gave 24.5 parts of crude "2-(4- bromophenylazo) -2.-nitropropane (9011 per cent yield), a yellowish-brown solid which was filtered in the cold. Recrystallization four times from 95 per cent ethyl alcohol gave'21;2 parts (78.3

per cent yield) of brownish-orange crystals.

"EXAMPLE .II I

A solution of 15.2 parts of' 4-nitro-2-aminotoluene,-35.7 parts of 38 per cent hydrochloric acid, and 625 parts of water, was diazotized at 25 C.,:by the dropwise addition of a solution of 7.5 parts of sodium nitrite in water. This acid solution of 3-nitrotoluene-2-diazonium chloride was then poured into a solution containing 20.7 parts ofsodium hydroxide, 250parts of water, and 200 parts of ice. A solution of 10.3 parts of Z-nitrobutane in L0 parts of sodium hydroxide and 125 parts of water was immediately added to the. slightly alkaline diazotized solution with thorough agitation. There resulted after sometime'a brilliant yellow powder which was filtered in the .cold. Recrystallization three times, from 95 per cent ethyl alcohol gave 19 parts (71.5 per cent yield) of 2-(2-methyl-B-nitro-phenylazo).- 2-nitrobutane, in the form of fine, fluffy yellow crystals.

, EXAMPLE III A solution of 19.7 parts of p-aminoaz'obenzene in 35.7 parts of 38 per cent hydrochloricacid and parts of water was poured in with stirring. I The resulting solution turned a brownish hue and aqueous alkali media, such; as are employed in large quantities of a brown powder separated and were filtered in the cold. Recrystallization two time from per cent ethyl alcoholgave,26.5 parts of 2-phenyl-(l-phenylenediazo) -2-nitropropane, a browncrystalline product corresponding to a-yieldof 89 per cent. x

-dium hydroxide and250 'partsof"waterwvasiadded re .cufdy:pr ipitate which 'rosei:=to'=';the-i1tgp; 613315 the...solution:;and wasffilteredirimthe xcold. i 'Recrystallization two timesffrom95*"perment1ethyl memo t A g 6 iitwtheeartsaixlargesgroup 'ricompounds whiclriare Azsolution of 28.7 parts of v-2-'naphtl lylamine in itnavel?fistmcturei?dit hich'iihelefoleimayfibe 71.5-Da1ts of 38 per centhydrochloric'iacid and utilized m synthesizing *mlmemus Other 11101191 125 parts of water was diazotize'd in the cold by "-9 Pu ution of parts l firtroswazoecompounds iproducediby our the *dropwise addition of a sol of3.sodiumgmtritezimmwter' .flhegmazotized S01u process retrelatively imsolubleiin zwater.zprovidt was thennmadegsfightiygaakafitne; by pouring angsof :rccurse; they FhaVeLrnQawater solubilizing the same, with agitation, into asolution of 41.3 gFwpsiisuchfiflswgawM, 0sM, and thezllk Parts or sosiumehydroiddesscosparts of 'water,, hereeiM'trepr-esentsihvdroeen. :a 0 )and 300 parts ofucrackeldiee. ailoealkaline earthcr metal. Therma -however;someneutralization previodslympzgpard 1 5 m, f whatssolublei' in alcohol; 2 acetone, andsbenzene. lmaipants pf zrtnitmpmpanezeEm-partsmt-Sm tmhesescompoundsifhave;:also' been found to pos- -=eesssgoodi-azfiinlty=for-wool, cotton and silk fibers, with stirring. -Therethemappeauedmirb nlprovidingsuitable' acidicprIbasicgroups .;are .tpresent nathe final azo compounds. These dyed fibersan yellowsbrowm orange and purple shades, sareooharacterized by :good 'rastness to washing, alcohol gave 31.5 parts (64.7 per cent yi'eldr of @flfingrefldifieht 7 2-(2-naphthylazo)-2-nitropropa e i th form Our invention snowihaving' been described,

of thin brownish-red plates. 0 What We claim is: V

1. In the manufacture of crystalline nitroazo EXAMPLE v compounds, the process which comprises diazo- Eighteen and forty-one hundredths parts of tizing in an acid medium a ring-substituted pribenzidine dissolved in 71.4 parts of 38 per cent y ar matic mine Which forms a diazo comhydrochloric acid and 125 parts of water was pound stable towards the alkaline aqueous mediazotized by adding dropwise thereto an aqueous dium employed in the subsequent coupling reacsolution containing 15 parts of sodium nitrite. tion, mixing and coupling the resulting diazo- The solution containing this diazotized product nium salt solution with a low-molecular-weight was then made alkaline by pouring the same into secondary nitroalkane in a cooled aqueous mea suspension of 200 parts of ice in a solution so dium of alkaline reaction containing suflicient consisting of 41.3 parts of sodium hydroxide and caustic alkali to neutralize said diazonium salt 500 parts of water. Immediately thereafter, a solution and to produce a pH at least as high as solution containing 17.8 parts of 2-nitropropane. that of an aqueous solution of an alkali metal 8 parts of sodium hydroxide and 250 parts of salt of said nitroalkane in order to ensure mainwater was added thereto. The resulting sclutenance of the nitroalkane in the form of its a1-.

tion became yellowish green, and when chilled kali metal salt during the coupling reaction and with ice yielded a greenish brown solid which recovering the resulting nitroazo compound. was filtered oh. This solid, after two recrystal- 2. In the manufacture of crystalline nitroazo lizations from 95 per cent ethyl alcohol, gave compounds, the process which comprises diazo- 35.5 parts, corresponding to a yield of 87.2 per tizing in an acid medium a ring-substituted pricent, of 4,4'-biphenyl-bis-(2-azo-2-nitropropane) mary aromatic amine which forms a diazo comin the form of dark brown needles. 7 pound stable towards the alkaline aqueous me- The data contained in the table below disclose dium employed in the subsequent coupling reaccertain physical properties of the compounds tion, neutralizing the resulting diazonium salt described in the preceding examples, as well as solution, cooling and mixing said solution with similar compounds not specifically described but an aqueous solution of an alkali meta1 salt of a prepared in accordance withthe procedures set lcw-molecular-weight secondary nitroalkane to forth above. produce coupling, the reaction medium having a Table Per Cent Nitrcgen Melting Compound Color P oiit,

Calcd. Found z-Nitrobenzene-(2-azo-2-nitropropane) 23. 5 23- 3 dark brown- 56. 9 3-Nitrobenzene-(2-azo-2-nitropropane) 23. 5 23. 6 yellow 71. 2-72. 2 3-Nitrobenzene-(2-azo-2-nitrobutane) 22. 2 22. 1 .do 63. 3-63. 7 2-Methyl-5-nitrobenzene-(2-azo-2-nitropropane 22. 2 22. 3 red-yellow. 70. 1 2Methyl-5-nitrobenzene-(2-azo-2-nitrobutane) 21. 0 21. 1 yellow 48. 9 4-Acetoamidobenzene-(2-azo-2-nitropropene). 22. 4 22. 3 yellow-brown 125. 3-125. 8 4-Ohlorobenzene- (2'azo-2-nitropropane) 18. 5 l8. 6 red-brown 67. 8 4-Bromobenzene- (2-azo-2-nitropropane) 15. 4 l 5. 4 brown-orange -91 2,5-Dichlorobenzene-(2-azo-2-nitropropane) 16. 1 l6. 2 57-58 2,.5-Dich1orobenzene-(2-azo-2-nitrobutane) 15. 3 15. 5 40-40. 3 2,4,6-Tribromobenzene-(2-azc-2-nitropropan 9. 8 9. 9 58. l 2,4,6-Tribromobenzene-(2-azo-2-nitrobutane) -1 9. 5 9. 6 57. 4-58 4-Methylbenzene-(2-azo-2-nitropropane) 20. 3 20. 4 20] 2-Oarboxybonzene-(2-azo 2-nitropropane) l7. 7 17. 8 orange-yellow 93. 2-93. 6 4-Carboxybenzene-(2azo-2-nitropropane) 17. 7 17. 8 yellow 16(3-169 ec. 4-Carboxybenzene-(2-azo-2-nitrobutane) 16. 7 l6. 9 do 1281433) ec. 2-I-4-Azo-(azobenzene)]-2-nitropropane 23. 5 23. 2 bro 1271-108 ec. 2-l-4-Azo-(azobenzene)1-2-nitrobutanc. 22. 5 22. 2 light brown. 80. 9-81. 4 4,4-Biphenyl-bis- (2-azo-2-mtropropane) 21. 9 21. 5 brown".-- 16221163. ()5

cc. l7. 3 l7. 1 purple-brown 67 2-Naphthylene-(2-azo-2-nitropropane) From the foregoing description it may be seen pH which is at least as high as that of an aqueous that the present invention has made available solution of said alkali metal salt to ensure main- 3. In the manufacture of crystalline nitroazo compounds, the process which comprises. diazo--1 tizing 'a biphenyl' amine, which forms adiazo compound stable towards the alkaline aqueous zxneclium employed in the subsequent coupling.reaction, mixing and coupling the resulting diazonium salt solution with a low-molecular-weight 10 secondary nitroalkanef in a cooled, aqueous medium containing sufilcient caustic alkali to neutralize said diazonium salt solution and to produce a pH at least as high as that of an aqueous solution of an alkali metal salt of said;.nitr0.-

alkane in order to ensure maintenance; of the nitroalkane in the form of its alkali metal salt during the couplin reaction, cooling andrecovering the resulting nitroazo compound.

v Meyer,

4. A nitro azonomnound'of the formula:

lotver alkyl' lower alkyl FRANKLIN DEGERING. f CHARLES F. FEASLEY.

REFERENCES CITED The following references are of record in the file'of this patent: Y. a I I Ambuhl, Ber. Deut. Chem. Gesell vol.

-8, page 1076.. 15'

, :c. F. Feasley et 'al., The Condensation of Aryl Diazonium Salts and or Hydroxides with Sec- ,ondar'yTNitro- Alkanes, Jour. .of Organic Chem, vo1. 8 ,1943..' 4 v a l a v 

